third_party/android_platform/bionic/tools/relocation_packer/src/packer.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "packer.h"
   6
   7 #include <vector>
   8
   9 #include "debug.h"
  10 #include "delta_encoder.h"
  11 #include "elf_traits.h"
  12 #include "leb128.h"
  13 #include "sleb128.h"
  14
  15 namespace relocation_packer {
  16
  17 // Pack relocations into a group encoded packed representation.
  18 template <typename ELF>
  19 void RelocationPacker<ELF>::PackRelocations(const std::vector<typename ELF::Rela>& relocations,
  20                                             std::vector<uint8_t>* packed) {
  21   // Run-length encode.
  22   std::vector<typename ELF::Addr> packed_words;
  23   RelocationDeltaCodec<ELF> codec;
  24   codec.Encode(relocations, &packed_words);
  25
  26   // If insufficient data do nothing.
  27   if (packed_words.empty())
  28     return;
  29
  30   Sleb128Encoder<typename ELF::Addr> sleb128_encoder;
  31   Leb128Encoder<typename ELF::Addr> leb128_encoder;
  32
  33   std::vector<uint8_t> leb128_packed;
  34   std::vector<uint8_t> sleb128_packed;
  35
  36   leb128_encoder.EnqueueAll(packed_words);
  37   leb128_encoder.GetEncoding(&leb128_packed);
  38
  39   sleb128_encoder.EnqueueAll(packed_words);
  40   sleb128_encoder.GetEncoding(&sleb128_packed);
  41
  42   // TODO (simonb): Estimate savings on current android system image and consider using
  43   // one encoder for all packed relocations to reduce complexity.
  44   if (leb128_packed.size() <= sleb128_packed.size()) {
  45     packed->push_back('A');
  46     packed->push_back('P');
  47     packed->push_back('U');
  48     packed->push_back('2');
  49     packed->insert(packed->end(), leb128_packed.begin(), leb128_packed.end());
  50   } else {
  51     packed->push_back('A');
  52     packed->push_back('P');
  53     packed->push_back('S');
  54     packed->push_back('2');
  55     packed->insert(packed->end(), sleb128_packed.begin(), sleb128_packed.end());
  56   }
  57 }
  58
  59 // Unpack relative relocations from a run-length encoded packed
  60 // representation.
  61 template <typename ELF>
  62 void RelocationPacker<ELF>::UnpackRelocations(
  63     const std::vector<uint8_t>& packed,
  64     std::vector<typename ELF::Rela>* relocations) {
  65
  66   std::vector<typename ELF::Addr> packed_words;
  67   CHECK(packed.size() > 4 &&
  68         packed[0] == 'A' &&
  69         packed[1] == 'P' &&
  70         (packed[2] == 'U' || packed[2] == 'S') &&
  71         packed[3] == '2');
  72
  73   if (packed[2] == 'U') {
  74     Leb128Decoder<typename ELF::Addr> decoder(packed, 4);
  75     decoder.DequeueAll(&packed_words);
  76   } else {
  77     Sleb128Decoder<typename ELF::Addr> decoder(packed, 4);
  78     decoder.DequeueAll(&packed_words);
  79   }
  80
  81   RelocationDeltaCodec<ELF> codec;
  82   codec.Decode(packed_words, relocations);
  83 }
  84
  85 template class RelocationPacker<ELF32_traits>;
  86 template class RelocationPacker<ELF64_traits>;
  87
  88 }  // namespace relocation_packer